1. Field of the Invention
The present invention relates to a method and apparatus for decoding a digital signal that has been error-correction encoded. More particularly, it relates to high-speed decoding of digital signals that have been encoded using optical signal processing technology.
2. Description of the Prior Art
In today's multimedia society in which large quantities of information have to be processed at high speed, information is digitized for recording and transmission and signals are error-correction encoded to eliminate errors arising in the course of signal recording and transmission. The received signals are decoded to extract the information. Conventional decoding uses a digital apparatus that employs semiconductor devices. JP-A 2001-7706, for example, describes an apparatus for the decoding of data that has been encoded using variable-length encoding, such as Huffman encoding. The apparatus is provided with two types of lookup tables, with one of the lookup tables being selected depending on the length of the variable-length code, and the code thereby decoded to a symbol value. This enables high-speed decoding and the use of lookup tables of smaller capacity.
However, this conventional technique cannot improve decoding speed when the encoding is fixed-length encoding, and also cannot provide an improvement in decoding speed that is in the order of several tens or several hundreds of times as fast. In the final analysis, digital processing using semiconductor devices is limited in terms of processing time and processing volume, and therefore does not provide a solution for dealing with the growing quantities of data being transmitted.
The object of the present invention is to provide a method and apparatus for decoding digital signals that can perform high-speed decoding without relying extensively on digital processing using semiconductor devices.